cosmos_python_ Python as calculator May 31, 2018

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1 cosmos_python_2018 May 31, Python as calculator Note: To convert ipynb to pdf file, use command: ipython nbconvert cosmos_python_2015.ipynb --to latex --post pdf In [3]: Out[3]: 4 In [4]: 3 * 90 Out[4]: 270 In [7]: * 6-2 Out[7]: 32 In [8]: 2/5.0 Out[8]: 0.4 In [1]: 2/5 Out[1]: New ideas: Modulo and whole value division In [10]: 8 % 3 Out[10]: 2 In [11]: 9 % 3 Out[11]: 0 In [12]: 8 // 3 Out[12]: 2 In [13]: 9 // 3 Out[13]: 3 1

2 2 Variables and Assignments In [3]: x = 6 type(x) Out[3]: int In [15]: x = 'My name is Joe' x Out[15]: 'My name is Joe' In [19]: type(x) Out[19]: str Note : variables are not "declared" as one type: variable type can change! In [20]: x = type(x) Out[20]: float In [21]: x = 1-3j type(x) Out[21]: complex In [22]: x = True type(x) Out[22]: bool In [5]: x, y = 3, 4 print (x,y) 3 4 In [7]: x, y = y, x print (x, y) 4 3 In [8]: z = x In [9]: x = z * y print (x, y, z)

3 In [34]: x = z - y print x, y, z In [10]: x = z**y - x print (x, y, z) In [36]: x = 2 y = 'Bob' x + y TypeError Traceback (most recent call last) <ipython-input-36-8d8b7d6f72c6> in <module>() 1 x = 2 2 y = 'Bob' ----> 3 x + y TypeError: unsupported operand type(s) for +: 'int' and 'str' In [37]: x = 'Bradley ' y = 'Cooper' x + y Out[37]: 'Bradley Cooper' In [12]: x = float(input("enter value for x:")) print ("The value of x is: ",x) Enter value for x:5 The value of x is: 5.0 In [16]: x, y = 2, 3 print ("The value of x * y = %d" % (x*y) ) The value of x * y = 6 3

4 2.1 Packages and modules In [17]: import numpy as np print (np.pi, np.cos(np.pi), np.e) In [18]: x = np.cos(np.pi) * np.sin(2*np.pi) + np.log(10) print ("x = %f" % (x) ) x = In [19]: import random as random #help(random) random.randint(0,9) Out[19]: Lists and Arrays All variables we have used to this point have had a single value. But we want a variable that supports multiple values at once : Called an "array" in C, python has a few different variable types with multiple values. here we will look at lists and arrays. Most basic type of container in python is a "list". It s just a list of quantities in a row, one after the other. What s special about python lists, is that all of the "elemnets" in the list do not have to be the same type Lists In [23]: r = [ 1, 2, 3, 4,5, 10] r Out[23]: [1, 2, 3, 4, 5, 10] In [21]: r = [ 'Bob', 6, 78.98, True, 10, 1+8j] r Out[21]: ['Bob', 6, 78.98, True, 10, (1+8j)] To add a new element to end of list, use "append": In [24]: r = [1, 2, 3, 4, 5, 10] r.append(6) r.append('apples') r Out[24]: [1, 2, 3, 4, 5, 10, 6, 'apples'] "Slicing" lets you access elements of the list 4

5 In [25]: r[3] Out[25]: 4 In [26]: r[3] = 'oranges' r Out[26]: [1, 2, 3, 'oranges', 5, 10, 6, 'apples'] In [27]: r[0:7] Out[27]: [1, 2, 3, 'oranges', 5, 10, 6] In [28]: r[-1] Out[28]: 'apples' In [29]: r[-1::-1] Out[29]: ['apples', 6, 10, 5, 'oranges', 3, 2, 1] In [36]: r_copy = r r_copy Out[36]: [99, 2, 3, 'oranges', 5, 10, 6, 'apples'] In [37]: r[0] = 86 r, r_copy Out[37]: ([86, 2, 3, 'oranges', 5, 10, 6, 'apples'], [86, 2, 3, 'oranges', 5, 10, 6, 'apples']) What happened? "r_copy" is not a separate copy of r. It "points" to r. We must be careful... If we want to separate copy of r, we must use slicing, as shown below. In [35]: # To create separate copy of a list r_copy = r[:] r_copy r[0] = 99 r, r_copy Out[35]: ([99, 2, 3, 'oranges', 5, 10, 6, 'apples'], [86, 2, 3, 'oranges', 5, 10, 6, 'apples']) In [38]: # Use range built-in function w = range(10) w Out[38]: range(0, 10) In [40]: w = list(range(1, 11)) w 5

6 Out[40]: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] In [42]: # get nuber of elements and sum of list w = list(range(1,100,10)) print (w) print ("Number of elements of w = ", len(w)) print ("Sum of all elements of w = ", sum(w)) [1, 11, 21, 31, 41, 51, 61, 71, 81, 91] Number of elements of w = 10 Sum of all elements of w = 460 In [46]: # Delete last element of list w = list(range(10)) print(w) w.pop() print(w) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] [0, 1, 2, 3, 4, 5, 6, 7, 8] Numpy arrays What if we want a "list" where all the elements are the same type (like in C language)? In python, this is called an array. Arrays use a special module called numpy ( for numerical python). Arrays are like vectors/matrices. They are fixed in length and work much faster than lists in python. We will use arrays more than lists. In [47]: # Import numpy module and create array of zeros import numpy as np array1 = np.zeros(10,float) print (array1, len(array1)) [ ] 10 In [48]: # Create array of ones of type integer array2 = np.ones(10,int) print (array2) [ ] In [49]: # Convert list to array ( and array to list) r = [1.2, 3.4, -1.5] # This is a list r_array = np.array(r) print (r_array) 6

7 [ ] In [50]: # Create 2D array (matrix) array3 = np.zeros((2,3)) # Notice (2,3) inside: 2 x 3 matrix print (array3) [[ ] [ ]] In [51]: # Operations on arrays array4 = np.array (range(10)) print ("Mean value in array = print ("Mean value in array = ", sum(array4)/ len(array4)) ", array4.mean()) Mean value in array = 4.5 Mean value in array = 4.5 In [52]: # Convert array to a list : To add onto array list4 = list(array4) print (list4) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] In [53]: # Arithmetic with arrays array5 = np.array([0,1,2, 3,4,5]) x = array5**2 print (x) [ ] In [54]: x = np.sqrt ( sum(array5**2)) print (x) Strings A string is a sequence of characters, usually used to store text In [60]: the_string = 'Hello World!' In [62]: the_string[4] the_string[:4] 7

8 Out[62]: 'Hell' In [81]: the_string.split() Out[81]: ['Hello', 'World!'] In [65]: the_string.split('r') Out[65]: ['Hello Wo', 'ld!'] In [67]: words = ['this', 'is', 'a', 'list', 'of', "strings"] ' '.join(words) Out[67]: 'this is a list of strings' In [69]: 'ABC'.join(words) Out[69]: 'thisabcisabcaabclistabcofabcstrings' In [71]: ''.join(words) Out[71]: 'thisisalistofstrings' Tuples Tuple consist of a numer of values separated by commas. They are useful for ordered pairs and returning several values from a funtion. In [89]: point1 = (3, 4, 5) print (point1) print(point1[0]) (3, 4, 5) 3 In [90]: x1,y1,z1 = point1 print(x1,y1,z1) # Unpacking a tuple Dictionaries Dictionaries are special types of python lists which allow lookup. We will use a dictionary when we look at converting DNA sequences to protein. In [91]: # Creating dictionaries num_dict = { 1: 'one', 2: 'two', 3: 'three', 4: 'four' } num_dict[3] #num_dict[5] num_dict[5]= 'five' num_dict[20] = 'twenty' print (num_dict.keys()) print (num_dict.values()) 8

9 dict_keys([1, 2, 3, 4, 5, 20]) dict_values(['one', 'two', 'three', 'four', 'five', 'twenty']) In [92]: print(num_dict.items()) for key,value in num_dict.items(): print (key,value) l = list(num_dict.items()) print(l) dict_items([(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four'), (5, 'five'), (20, 'twenty')]) 1 one 2 two 3 three 4 four 5 five 20 twenty [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four'), (5, 'five'), (20, 'twenty')] 2.3 Simple plotting with "matplotlib" In [56]: # Define x-axis and y-axis with arrays of points import numpy as np x = np.arange(0, 2*np.pi,.1) # Like range for lists print (x) y = np.sin(x) print (y) [ ] [ ] In [57]: # Now import matplotlib library and plot import matplotlib.pyplot as plt 9

10 plt.plot(x,y) plt.show() In [58]: # Make plot fancier with title, labels plt.plot(x,y, 'r') plt.title('plot of x vs sin(x)') plt.xlabel('x') plt.ylabel('sin(x)') plt.show() 10

11 Go to matplotlib gallery on internet for examples!! 11

The SciPy Stack. Jay Summet

The SciPy Stack. Jay Summet The SciPy Stack Jay Summet May 1, 2014 Outline Numpy - Arrays, Linear Algebra, Vector Ops MatPlotLib - Data Plotting SciPy - Optimization, Scientific functions TITLE OF PRESENTATION 2 What is Numpy? 3rd